Method for preparing acrylonitrile



United States Patent 3,326,961 METHOD FOR PREPARING ACRYLONITRILE Jamal S. Eden, Akron, Ohio, and Charles E. Ziegler, Therwil, Basel-Land, Switzerland, assignors to The B. F. Goodrich Company, New York, N.Y., a corporation of New York No Drawing. Original application Jan. 27, 1964, Ser. No. 340,533. Divided and this application July 8, 1966, Ser. No. 571,371

6 Claims. (Cl. 260-465.3)

This is a division of application Ser. No. 340,533 filed I an. 27, 1964.

This invention relates to a method of preparing acrylonitrile from propylene, an oxygen containing .gas and ammonia at elevated temperatures in the presence of an oxidation catalyst containing tellurium and rhenium and to the catalyst itself. More particularly, the invention relates to a method of preparing acrylonitrile in one step by passing a mixture of propylene, an oxygen containing gas, wammounia and, desirably, water vapor over a catalyst comprising a molybdate or phosphomolybdate containing a tellurium and a rhen-ium compound at a temperature of from about 350 to about 500 C.

The vapor phase preparation of acrylonitrile from propylene, oxygen, ammonia and water vapor in the presence of bismuth and antimony molybdates or phosphomolybdates and bismuth phosphotungstate at temperatures of from 500 F. to 1000 F. is described in US :Patent 2,904,580.

It has been found that if certain tellurium and rhenium compounds are added to certain molybdate or phosphomolybdate, particularly those of bismuth and tin, the yields of acrylonitrile are increased greatly, and, if the catalyst is prepared in a proper way, the production of by-products, acetonitrile and HCN, is suppressed almost completely. The acetonitrile and HCN are undesirable, because they must be removed from the acrylonitrile and the purification step can be very difiicult, particularly if some acrolein is also formed as a by-product, in which case an acrolein cyanohydrin is formed with HCN. In addition, the amounts of HCN and acetonitrile usually formed in the reaction are such that economical recovery is not possible, yet the amounts are sufiicient to cause serious disposal problems of refuse from the purification step. Because of their solubility in water and their toxicity they must either be converted to non-toxic products as by hydrolysis or they must be removed from the water prior to disposal through usual sewage systems.

The overall desired reaction of this invention can be written empirically as follows:

There are, however, several competing reactions which can consume some oxygen or ammonia or both. Invariably some oxides of carbon and nitrogen are also formed during the reaction. Nevertheless, it is possible to obtain acrylonitrile in fair yields at ratios of propylene to NH as low as 1 to 0.5, but, preferably, the ratio should be at least 1 to 1 and more desirably about 1 to 2 to obtain maximum yields.

The oxygen to propylene ratio is not particularly critical, but in order to get good conversion and yields it 3,326,961 Patented June 20, I967 ice PROCEDURE 1 In this procedure the catalyst was prepared from a slurry of molybdic acid by adding a bismuth salt, tellurium oxide and perrhenic acid thereto. It was supported on a silica base and contained the following:

Ingredient: Amount Bi(NO -5H O g 58.2 M00 g 27.2 Te0 g 5.74 HReO g .30 H PO (85%) g .93 Silica (Ludox HS) g 75.0 H O ml 80 HNO (conc.) ml 4 Ludox HS is an aqueous dispersion of silica containing about 30% SiO2 and the remainder is essentially all water. It has an SiOz/NmO ratio of about 95, a pH of 9.8 and an average particle size of about 15 microns.

The nitric acid was first added to the water and then the M00 was added to the acid solution. The bismuth nitrate was then added to the M00 slurry and finally the H PO HReO and Te0 were added. The mixture at this stage was a slurry, believed to contain bismuth phosphomolybdate perrhenic acid and tellurium oxide. This mixture was then added to the Ludox dispersion and dried in air at about C. After drying, the catalyst was baked in an air oven for about 16 hours at approximately 400 C. It was then ground and screened to pass through sieves of 10-1-8 mesh (U.S.).

PROCEDURE 2 Amount The nitric acid was added to 150 ml. water. The perrhenic acid was dissolved in 2 ml. water and TeO was dissolved in 58 ml. hot HCl and filtered. The ammonium molybdate 'was dissolved in 680 ml. water, with the aid of heat and stirring and the addition of 20 ml. of the aqueous nitric acid solution. The bismuth nitrate was dissolved in ml. of the aqueous nitric acid solution with stirring and heating.

The silica dispersion was placed in an evaporating dish on a steam bath. Then the TeO HReO and H PO were added and stirred thoroughly. The ammonium molybdate solution was added to the above mixture and finally the bismuth nitrate solution was added. Up to the point of the addition of the bismuth nitrate all the ingredients except the silica remained in solution. On addition of the bismuth nitrate the formation ,of a bismuth phosphomolybdate slurry resulted. The final mixture was stirred well and dried in an air oven at 100 C. and then 3 baked for 16 hours at about 40 C. The catalyst was then ground and passed through a 18 mesh sieve (U.S.).

PROCEDURE 3 The bismuth nitrate was dissolved in the nitric acid. The ammonium molybdate was added to 680 ml. of water and 20 ml. of the HNO solution were added to dissolve the ammonium molybdate. The perrhenic acid was dissolved in 2 ml. water and added to the ammonium molybdate solution. The latter solution was stirred while the silica 'was added. Then 250 ml. water were added to the silicamolybdate-perrhenic acid mixture to form a fluid paste. The Te'O was dissolved in the HCl and filtered and then added to the silica containing slurry. The bismuth nitrate solution was added to the silica slurry and finally the H PO was mixed into the catalyst. On addition of the H PO a precipitate forms which coats uniformly the silica particles. The final color of the catalyst was a deep yellow. The catalyst was dried on a steam bath and then baked in an oven at 400 C.

Other. phosphomolybdate catalysts containing tin or antimony can be prepared by following the above procedures.

For the purpose of this application the catalysts prepared by procedures 2 and 3 above are termed homogeneous catalysts because all the ingredients except silica are in solution until the addition of the final ingredient which effects precipitation on the support.

The catalysts can be used either with or without supports, although support is preferred. In addition, the catalyst can be employed in either a fixed or fluidized bed. The fluidized bed process provides means for better temperature control and minimizes development of hot spots and for this reason is more desirable than the fixed bed operation.

In addition to silica, other finely divided supports can be used. These include alumina, silicon carbide, clays, diatomaceous earth, etc. Of these supports, silica is most desirable because of its comparatively low cost, uniformity of composition and particle size and ready availability.

The contact time can vary between about 1 to about 40 seconds, but for best results contact times of to about 30 seconds are most satisfactory.

Surprisingly, excellent conversions of propylene and yields of acrylonitrile are obtained at temperatures as low as about 350 C. but the preferred temperature range is 400-425 C.

The examples which follow are intended to illustrate the invention and not as limitations thereon.

Example I A catalyst prepared by procedure 2 above was used in this run. The molar ratio of ingredients in the catalyst were bismuth phosphomolybdate 100, Te0 30, HReO 1, silica 250.

Sixty ml. of catalyst of 10-18 U.S. screen mesh were placed in a reactor made of high silica glass (Vycor) tube having an internal diameter of inch. The catalyst filled a depth of about 6 inches in the tube.

; The reactor had three inlets, one for a mixture of propylene and oxygen, one for water vapor, and one for ammonia, which can be either in gaseous or vapor form as concentrated NH OH. The reactor was equipped with a movable thermocouple, so that the temperature at any part of the unit in which the reaction was occurring could HCN be measured. The outlet from the reactor was connected to a drying tube to remove water. Gases which passed through the drying tube were passed through a vapor phase chromatograph (Perkin-Elmer) Vapor Refractometer, model 154) for continuous analysis of gaseous effluent from the reactor. The reactor was provided with electrical heating elements to preheat the ingredients entering the reaction zone and to maintain the desired temperature. Variable amounts of catalyst can be used and the catalyst can be in a fixed or fluidized bed. For fluid bed systems the amount of catalyst used will vary somewhat depending on the velocity of gases being fed into the reactor, the contact time and the length of the reactor. The quantity of catalyst, however, should form a bed at least about 6 inches high and the maximum height is not critical, but it should be adjusted to avoid excessive loss of catalyst from the reactor by the stream velocity.

A mixture of air and propylene in a ratio of 68.3 volumes of air to 7.1 of propylene was prepared and fed into the reactor at a rate of 5.9 liters per hour. Water at the rate of .06 mol and ammonia at the rate of .025 mol per hour were also fed simultaneously with the propyleneoxygen mixture. The entire mass of feed stock was heated to ZOO-250 C. before contacting the catalyst, which was preheated to 450 C. and held at 400450 C. during the run. The contact time was about 30 seconds. The temperature recorded at various portions of the reactor varied from 400 C. at the first inch of the bed to 445 C. at 3 /2 inches from the inlet and 420 C. at the top of the bed.

The dry gaseous reaction efiiuent contained the following mol percent of ingredients. N 81.0, O 2.5, acrylonitrile 8.5 acetonitrile 1.24; CO0.2; CO 3.1; HCN1.28; and propylene 2.06. From these values it was calculated that the conversion of propylene was 84.1% and the yield of acrylonitrile, based on the propylene converted was 77.77 This gives an efficiency of 65.5% for acrylonitrile.

Examples II-IIl In these exmaples a non-homogeneous bismuth phosphomolybdate-TeO -HReO catalyst prepared by procedure 1 with a molar ratio of 100, 30 and 1 respectively and 250 mols silica was used. The amount of catalyst was sufiicient to fill 6 inches of the reactor. The data below show the reaction conditions and results obtained.

II III Oz/propylene H2O] ropy1ene NHa propylene Contact time (see.) Temp. C Propylene Conversion. Yield of acrylonitrile Efiieiency Acetonitrile.

Examples I V-V Oz/prOpylene H20/ r0pylene NHJpropylene Contact time (sec) Temp. C Propylene Conversion- Aerylonitrile yield a In each of the above examples small amounts of acrolein were formed. This could be recovered easily and recycled with the propylene feed for producing acrylonitrile.

.3 370-400 C. with a Contact time of 20 Seconds. End

' product analysis showed a propylene conversion of 49.5

a yield of acrylonitrile of 89.3% and an efiiciency of 44.5%. When a catalyst containing no rhenium was sub- Example VI stituted, and the above mixture was reacted at 410 C. u a he propylene conversion dropped to 39.4% with an A homo eneous catal st made b rocedure 2 but t using twice amount HReO4 wispemployed' This acrylonitrile yield of 93.2% for an efiiciency of 36.7%. represents a homogeneous catalyst on a silica support. Example XXI The feed stock based on propylene as unity was in a ratio A h V omogeneous catalyst was prepared by procedure 2 of 21/2 Parts of y 2 Parts ammoma and Pains using the following molar ratios of ingredients: M00 of water. Contact time was 20 seconds and the reaction (75) SH (25) Te (25) P 07 (3) Re (1) and Si (250) temperature was 4200 The conversion of propylene The tin salt employed was snCl O The catal st was was 67.2% with an acrylonitrile yield' of 81.2% to give h 1 bd t t 4 t fi d i an efficiency of 546 Only about 06% CH CN was m P-oSP omo-y ac a-lnlng e unum an r emum formed in {11.5 reacti'ol'l 3 as oxides. A mixture containing 2.5 mols oxygen, 4.1 mols 1 water vapor, 1.05 mols ammonia and 1 mol of propylene Examples VII-XI was passed through a 6 inch layer of catalyst at a tempera- In this set of runs a homogeneous catalyst prepared in i of 420 Wlth a Contact tune of 18 seconds Analyaccordance with procedure 2 was used. The reaction data SIS of end products showed that the propylene converslon are given below. 20

VII VIII IX X XI Oz/propylene 2 2. 5 2. 5 2. 5 2. 5 Bro/propylene" 2. 2 3. 6 3. 6 3. 6 2. 2 NHe/propylene 1. 5 1. 5 1. 5 2 1 Contact time (sec.) 20 18 18 20 20 Temp. 0 4042425 430 440 440 445 Propylene Conversiom. 62.9 74. 4 73. 5 71. 5 67. 3 Acrylonitrile yield 86. 6 73. 2 77. 1 83. 6 80. s 54. 4 54. 4 56. 6 59.8 54. 2

Examples XII-X VIII In these runs the same catalyst as that described in the immediately preceding examples was used. The catalyst was not removed from the reactor over a period of was 90.1% with an acrylonitrile yield of 84.0%, for an etliciency of 75.8%.

Example XXII A tin molybdate catalyst, having a molar ratio of 75 hours of actual use to show that catalyst life is maintained 40 M 003 SD: 15 e and 02 Re on 125 mols of colloidal over a long period of time.

XII XIII XIV I XV XVI I XVII XVIII Orlpropylene 2 2. 5 2. 5 3 3 3 3 E o/propylene 3. 6 3. 6 3. 6 4. 8 4.8 5.0 5.0 NHa/propylene. 1. 5 1. 5 1. 5 2. 0 2 2 2 Contact time (se 31 27 27 22 22 29 29 Temp. C 400 430 450 450 445 450 450 Propylene Conversion 60.8 76.9 88. 3 95. 4 89. 6 94.8 90. 6 Acrylonitrile yield 83. 9 84 76. 2 52. 8 70. 4 80. 0 79. 8 Efficiency 51 67. 3 50. 3 63. 0 75. 8 72. 3 CHaCN- 0.8 0.4 HON 0 0 Example XIX A homogeneous catalyst made by the process of procedure 2 was used. The feed into the reactor consisted of a mixture of 75% propylene and 25% propane by volume. The ratio of oxygen and ammonia to propylene were 2.5 to 1 and 1 to 1, respectively. The water vapor ratio was 4 based on propylene. This reaction was run at 440 C. with a contact time of 20 seconds. Analysis showed a propylene conversion of 59.8%, a yield of acrylonitrile of 87.5% and an etficiency of 52.3%. From these data it is apparent that saturated gaseous hydrocarbons do not interfere with the catalytic conversion of propylene to acrylonitrile.

Example XX silica, was used in this example. The NH /C H ratio was 1, and the O /C H ratio was 2.5. The cold contact time was 18 seconds and temperature varied between 110 and 42 0 C. The reaction conditions were otherwise the same as those of example XXI, in a fixed bed system. The propylene converted was 98.9% with an 82.1% yield of acrylonitrile for an efliciency of 81.2%.

Other catalysts, using molar ratios of TeO of 10 to 50* and HReO of 1 to 10 per mols of bismuth, antimony or tin phosphomolybdate, can also be used to convert propylene to acrylonitrile but there is no significant change in results in using the higher ratios of tellurium or rhenium. However, it is essential that both tellurium and rhenium be present, because the lack of one of these two ingredients results in considerable lower activity for the catalyst.

We claim:

1. A method of preparing acrylonitrile comprising passing a mixture in a molar ratio, per mol of propylene, of an oxygen containing gas in sufiicient quantity to provide about 1.5 to about 3 mols of oxygen, from about 1 to about 2 mols of ammonia and up, to about 5 mols of Water vapor through a bed of a catalyst consisting essentially of a mixture of (1) tellurium oxide and (2) rhenium oxide and bismuthphosphomolybdate, antimony phosphomolybdate, tin phosphomolybdate or tin molybdate in a ratio of 1-10 mols of rhenium oxide calculated as HReO and .10-50 mols of TeOg per 100 mols of said phosphomolybdates and tin molybdate, at a temperature of from about 350 to about 500 C. with a contact time of from about 1 to about 40 seconds.

2. The method of claim 1 in Which the catalyst ratio is 100 mols bismuth phosphomolybdate and 12, of rhenium oxide. calculated as HReO 3. The methodof claim 1 in which the phosphomolybdate is tin phosphomolybdate.

4. The method of claim 1 in which tin molybdate is a catalyst component.

5. A method of preparing acrylonitrile comprising passing a mixture in amolar ratio of one mol of propylene,

sufiicient air to provide 2-3 mols of oxygen per mol of propylene, from about 3.5 to about 5 mols of water vapor per mol of propylene and from 1.25 to 2 mols of ammonia per mol of propylene through a bed of catalyst consisting essentially of a molar ratio of 100 bismuth phosphomolybdate, 30 TeO and one rhenium oxide calculated as HReO at a temperature of from about 400 450 C. and a contact time of from about 18 to about 30 seconds.

6. A method of preparing acrylonitrile comprising passing a mixture containing, on a molar basis, about 1 mol of propylene, about 1.05 mols of ammonia, about 4.1 mols of water vapor and sufiicient air to provide 2.5 mols of oxygen, through a bed of catalyst consisting essentially of, on a molar basis, 25 tin phosphomolybdate, 25 TeO and one rhenium oxide calculated as HReO at a temperature of about 420 C. and a contact time of about 18 seconds.

No references cited.

CHARLES B. PARKER, Primary Examiner. J. P. BRUST, Assistant Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,326,961 June 20, 1967 Hamal S. Eden et a1.

It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 3, line 1, for "40C." read 400C. column 4, line 59, for "exmaples" read examples column 6, line 3. for "89.3%" read 89.8% line 57, for "110" read Signed and sealed this 13th day of August 1968.

(SEAL) Attest:

EDWARD J. BRENNER Commissioner of Patents Edward M. Fletcher, Jr.

Attesting Officer 

1. A METHOD OF PREPARING ACRYLONITRILE COMPRISING PASSING A MIXTURE IN A MOLAR RATIO, PER MOL OF PROPYLENE, OF AN OXYGEN CONTAINING GAS IN SUFFICIENT QUANTITY TO PROVIDE ABOUT 1.5 TO ABOUT 3 MOLS OF OXYGEN, FROM ABOUT 1 TO ABOUT 2 MOLS OF AMMONIA AND UP TO ABOUT 5 MOLS OF WATER VAPOR THROUGH A BED OF A CATALYST CONSISTING ESSENTIALLY OF A MIXTURE OF (1) TELLURIUM OXIDE AND (2) RHENIUM OXIDE AND BISMUTH PHOSPHOMOLYBDATE, ANTIMONY PHOSPHOMOLYBDATE, TIN PHOSPHOMOLYBDATE OR TIN MOLYBDATE IN A RATIO OF 1-10 MOLS OF RHENIUM OXIDE CALCULATED AS HREO4 AND 10-50 MOLS OF TEO2 PER 100 MOLS OF SAID PHOSPHOMOLYBDATES AND TIN MILYBDATE, AT A TEMPERATURE OF FROM ABOUT 350* TO ABOUT 500*C. WITH A CONTACT TIME OF FROM ABOUT 1 TO ABOUT 40 SECONDS. 